Monitoring the efficacy of chemotherapy in children with acute lymphobastic leukemia (ALL) is difficult and requires bone marrow biopsy. We hope to develop a means of estimating the efficacy of chemotherapy non-invasively using 1H NMR spectroscopy. Mountford et al. has shown that malignant lymphocytes contain significantly larger amounts (6%) of membrane bound neutral triglycerides as compared to nonmalignant lymphocytes. The larger amount of membrane triglyceride correlates to increased membrane fluidity which in turn generates well defined 1H MR spectra unique to malignant cells. We wished to determine if the malignant lipid membrane 1H spectra changed after drug treatment in vitro. Methods The malignant T-cell lines: Jurkat, NKJY, and Hut 78, and the B-cell line: BUR (Burkitt~s lymphoma) were grown in the logarithmic growth phase using standard cell culture techniques. Cultures were treated with Doxorubicin (200 ng/ml for 48 hours). The Jurkat line was also treated with Dexamethasone (25 ~M for 72 hours), fetal calf serum deprived media (for 72 hours), and fracture-freezing (10 minutes of exposure to dry ice). 5 x l0~ cells of each sample was analyzed on a Bruker CSI Omega 400mHz high resolution spectrometer. There was a twofold increase in the absolute peak intensities of the methylene resonance (1.3 ppm) in the treated versus non-treated cells of all four cell lines. The increase in the methylene peak intensities temporally correlated to the start of programmed cell death (apoptosis) as determined by nuclear stains and the appearance of DNA ladder formation on electrophoretic gels. Non-apoptotic cell death (necrosis) induced by freezing did not result in any spectral change from control cultures. Results and Discussion 1H NMR spectroscopy can detect and monitor leukemic cell death in vitro. The appearance of cell death (apoptosis) is concurrent with a twofold increase in the amount of available methylene protons within the plasma membrane. It is possible that 1H NMR spectroscopy can be used to monitor in vivo the early effects of chemotherapy in children with ALL.